Method and system of multi-layer beamforming

ABSTRACT

A base station includes a reference signal sequence generator configured to generate a reference signal sequence for a reference signal for each of n antenna ports using one initialization seed c init  with n being a positive integer. The initialization seed is defined as:
 
 c   init =(└ n   s /2┘+1)·(2 N   ID   cell +1)·2 16   +N   ID   group ,
 
where n s  is a first slot number in a subframe, N ID   cell  is a cell identifier of the base station, and N ID   group  is a group identifier. The base station also includes a transmit path circuitry configured to transmit a downlink grant and the reference signal. In some embodiments, the group identifier N ID   group  is a one-bit group identifier dynamically indicated in a codepoint in the downlink grant transmitted by the base station.

CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY

The present application is related to U.S. Provisional PatentApplication No. 61/250,782, filed Oct. 12, 2009, entitled “MULTI-USERMIMO TRANSMISSIONS AND SIGNALING IN WIRELESS COMMUNICATION SYSTEMS” andU.S. Provisional Patent Application No. 61/278,835, filed Oct. 13, 2009,entitled “MULTI-LAYER BEAMFORMING METHODS IN WIRELESS COMMUNICATIONSYSTEMS”. Provisional Patent Application Nos. 61/250,782 and 61/278,835are assigned to the assignee of the present application and are herebyincorporated by reference into the present application as if fully setforth herein. The present application hereby claims priority under 35U.S.C. §119(e) to U.S. Provisional Patent Application Nos. 61/250,782and 61/278,835.

TECHNICAL FIELD

The present application relates generally to wireless communicationsand, more specifically, to a method and system for multi-layerbeamforming.

BACKGROUND

In 3^(rd) Generation Partnership Project Long Term Evolution (3GPP LTE),Orthogonal Frequency Division Multiplexing (OFDM) is adopted as adownlink (DL) transmission scheme.

SUMMARY

A base station is provided. The base station comprises a referencesignal sequence generator configured to generate a reference signalsequence for a reference signal for each of n antenna ports using oneinitialization seed c_(init) with n being a positive integer. Theinitialization seed is defined as:c _(init)=(└n _(s)/2┘+1)·(2N _(ID) ^(cell)+1)·2¹⁶ +N _(ID) ^(group),where n_(s) is a first slot number in a subframe, N_(ID) ^(cell) is acell identifier of the base station, and N_(ID) ^(group) is a groupidentifier. The base station also comprises a transmit path circuitryconfigured to transmit a downlink grant and the reference signal.

A method of operating a base station is provided. The method comprisesgenerating a reference signal sequence for a reference signal for eachof n antenna ports using one initialization seed c_(init) with n being apositive integer. The initialization seed is defined as:c _(init)=(└n _(s)/2┘+1)·(2N _(ID) ^(cell)+1)·2¹⁶ +N _(ID) ^(group),where n_(s) is a first slot number in a subframe, N_(ID) ^(cell) is acell identifier of the base station, and N_(ID) ^(group) is a groupidentifier. The method also comprises transmitting a downlink grant andthe reference signal.

A subscriber station is provided. The subscriber station comprises areceive path circuitry configured to receive a downlink grant from abase station. The receive path circuitry is also configured to receive areference signal generated at the base station using one initializationseed c_(init). The initialization seed is defined as:c _(init)=(└n _(s)/2┘+1)·(2N _(ID) ^(cell)+1)·2¹⁶ +N _(ID) ^(group),where n_(s) is a first slot number in a subframe, N_(ID) ^(cell) is acell identifier of the base station, N_(ID) ^(cell) is a groupidentifier.

A method of operating a subscriber station is provided. The methodcomprising receiving a downlink grant from a base station, and receivinga reference signal generated at the base station using oneinitialization seed c_(init). The initialization seed is defined as:c _(init)=(└n _(s)/2┘+1)·(2N _(ID) ^(cell)+1)·2¹⁶ +N _(ID) ^(group),where n_(S) is a first slot number in a subframe, N_(ID) ^(cell) is acell identifier of the base station, and N_(ID) ^(group) is a groupidentifier.

In some embodiments, the group identifier N_(ID) ^(group) is a one-bitgroup identifier dynamically indicated in a codepoint in the downlinkgrant transmitted by the base station.

Before undertaking the DETAILED DESCRIPTION below, it may beadvantageous to set forth definitions of certain words and phrases usedthroughout this patent document: the terms “include” and “comprise,” aswell as derivatives thereof, mean inclusion without limitation; the term“or,” is inclusive, meaning and/or; the phrases “associated with” and“associated therewith,” as well as derivatives thereof, may mean toinclude, be included within, interconnect with, contain, be containedwithin, connect to or with, couple to or with, be communicable with,cooperate with, interleave, juxtapose, be proximate to, be bound to orwith, have, have a property of, or the like; and the term “controller”means any device, system or part thereof that controls at least oneoperation, such a device may be implemented in hardware, firmware orsoftware, or some combination of at least two of the same. It should benoted that the functionality associated with any particular controllermay be centralized or distributed, whether locally or remotely.Definitions for certain words and phrases are provided throughout thispatent document, those of ordinary skill in the art should understandthat in many, if not most instances, such definitions apply to prior, aswell as future uses of such defined words and phrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

FIG. 1 illustrates an exemplary wireless network that transmits messagesin the uplink according to the principles of this disclosure;

FIG. 2 is a high-level diagram of an orthogonal frequency divisionmultiple access (OFDMA) transmitter according to one embodiment of thisdisclosure;

FIG. 3 is a high-level diagram of an OFDMA receiver according to oneembodiment of this disclosure;

FIG. 4 illustrates a diagram of a base station in communication with aplurality of mobile stations according to an embodiment of thisdisclosure;

FIG. 5 illustrates a spatial division multiple access (SDMA) schemeaccording to an embodiment of this disclosure;

FIGS. 6A and 6B illustrate reference signal patterns according to anembodiment of this disclosure;

FIG. 7 illustrates data sections and reference signal sections of areference pattern shown in FIG. 6 from the perspective of two userequipments according to an embodiment of this disclosure;

FIG. 8 illustrates data sections and reference signal sections of thereference pattern shown in FIGS. 6A and 6B from the perspective of twouser equipments (UEs) according to another embodiment of thisdisclosure;

FIG. 9 illustrates a table summarizing downlink control information(DCI) formats used for downlink (DL) grants according to an embodimentof this disclosure;

FIG. 10 illustrates a table showing a mapping of enabled codewords to astream index and a dedicated reference signal (DRS) index according toan embodiment of this disclosure;

FIG. 11 illustrates a table showing a mapping of a new data indicator(NDI) bit of a disabled codeword to a stream index and a dedicatedreference signal (DRS) index according to an embodiment of thisdisclosure;

FIG. 12 illustrates a system for generating and mapping reference signalsequences according to an embodiment of this disclosure;

FIG. 13 illustrates a method of operating an enhanced Node B (eNodeB) orbase station according to an embodiment of this disclosure;

FIG. 14 illustrates a method of operating a UE or mobile stationaccording to an embodiment of this disclosure;

FIG. 15 illustrates a table depicting two states in a downlink (DL)grant according to an embodiment of this disclosure;

FIG. 16 illustrates a table depicting two states in a downlink (DL)grant using a one-bit field according to an embodiment of thisdisclosure;

FIG. 17 illustrates a table summarizing the indication of the DRSscrambling method as a function of the DCI format, the number of enabledtransport blocks (TBs) and the transmission mode according to anembodiment of this disclosure;

FIG. 18 illustrates a table depicting two states in a downlink (DL)grant according to another embodiment of this disclosure;

FIG. 19 illustrates a table depicting two states in a downlink (DL)grant using a one-bit field according to another embodiment of thisdisclosure;

FIG. 20 illustrates a table summarizing the indication of the DRSscrambling method as a function of the DCI format, the number of enabledTBs and the transmission mode according to another embodiment of thisdisclosure;

FIG. 21 illustrates a table depicting use of an existing bit in aparticular downlink (DL) grant to indicate the choice of cell-specificscrambling or UE-specific scrambling according to an embodiment of thisdisclosure;

FIG. 22 illustrates a method of operating an eNodeB or base stationaccording to another embodiment of this disclosure;

FIG. 23 illustrates a method of operating a UE or mobile stationaccording to an embodiment of this disclosure;

FIG. 24 illustrates a method of operating an eNodeB or base stationaccording to a further embodiment of this disclosure;

FIG. 25 illustrates a method of operating a UE or mobile stationaccording to an embodiment of this disclosure;

FIG. 26 illustrates a table summarizing a method of indicating a groupid and a stream index using the DCI format 2B according to an embodimentof this disclosure;

FIG. 27 illustrates a table summarizing a method of indicating a groupid and a stream index using the DCI format 2B according to anotherembodiment of this disclosure;

FIG. 28 illustrates a table summarizing a method of indicating a groupid and a stream index using the DCI format 1E according to an embodimentof this disclosure;

FIG. 29 illustrates a table summarizing a method of indicating a groupid and a stream index using the DCI format 1E according to anotherembodiment of this disclosure;

FIG. 30 illustrates a linkage between a location of a control channelelement (CCE) aggregation and a group id according to an embodiment ofthis disclosure;

FIG. 31 illustrates a method of operating an eNodeB or base stationaccording to yet another embodiment of this disclosure; and

FIG. 32 illustrates a method of operating a UE or mobile stationaccording to yet another embodiment of this disclosure.

DETAILED DESCRIPTION

FIGS. 1 through 32, discussed below, and the various embodiments used todescribe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged wireless communication system.

With regard to the following description, it is noted that the long termevolution (LTE) term “node B” is another term for “base station” usedbelow. Also, the LTE term “user equipment” or “UE” is another term for“subscriber station” used below.

FIG. 1 illustrates exemplary wireless network 100, which transmitsmessages according to the principles of the present disclosure. In theillustrated embodiment, wireless network 100 includes base station (BS)101, base station (BS) 102, base station (BS) 103, and other similarbase stations (not shown).

Base station 101 is in communication with Internet 130 or a similarIP-based network (not shown).

Base station 102 provides wireless broadband access to Internet 130 to afirst plurality of subscriber stations within coverage area 120 of basestation 102. The first plurality of subscriber stations includessubscriber station 111, which may be located in a small business (SB),subscriber station 112, which may be located in an enterprise (E),subscriber station 113, which may be located in a wireless fidelity(WiFi) hotspot (HS), subscriber station 114, which may be located in afirst residence (R), subscriber station 115, which may be located in asecond residence (R), and subscriber station 116, which may be a mobiledevice (M), such as a cell phone, a wireless laptop, a wireless personaldata or digital assistant (PDA), or the like.

Base station 103 provides wireless broadband access to Internet 130 to asecond plurality of subscriber stations within coverage area 125 of basestation 103. The second plurality of subscriber stations includessubscriber station 115 and subscriber station 116. In an exemplaryembodiment, base stations 101-103 may communicate with each other andwith subscriber stations 111-116 using OFDM or OFDMA techniques.

While only six subscriber stations are depicted in FIG. 1, it isunderstood that wireless network 100 may provide wireless broadbandaccess to additional subscriber stations. It is noted that subscriberstation 115 and subscriber station 116 are located on the edges of bothcoverage area 120 and coverage area 125. Subscriber station 115 andsubscriber station 116 each communicate with both base station 102 andbase station 103 and may be said to be operating in handoff mode, asknown to those of skill in the art.

Subscriber stations 111-116 may access voice, data, video, videoconferencing, and/or other broadband services via Internet 130. In anexemplary embodiment, one or more of subscriber stations 111-116 may beassociated with an access point (AP) of a WiFi wireless local areanetwork (WLAN). Subscriber station 116 may be any of a number of mobiledevices, including a wireless-enabled laptop computer, personal dataassistant, notebook, handheld device, or other wireless-enabled device.Subscriber stations 114 and 115 may be, for example, a wireless-enabledpersonal computer (PC), a laptop computer, a gateway, or another device.

FIG. 2 is a high-level diagram of an orthogonal frequency divisionmultiple access (OFDMA) transmit path 200. FIG. 3 is a high-leveldiagram of an orthogonal frequency division multiple access (OFDMA)receive path 300. In FIGS. 2 and 3, the OFDMA transmit path 200 isimplemented in base station (BS) 102 and the OFDMA receive path 300 isimplemented in subscriber station (SS) 116 for the purposes ofillustration and explanation only. However, it will be understood bythose skilled in the art that the OFDMA receive path 300 may also beimplemented in BS 102 and the OFDMA transmit path 200 may be implementedin SS 116.

The transmit path 200 in BS 102 comprises a channel coding andmodulation block 205, a serial-to-parallel (S-to-P) block 210, a Size NInverse Fast Fourier Transform (IFFT) block 215, a parallel-to-serial(P-to-S) block 220, an add cyclic prefix block 225, an up-converter (UC)230, a reference signal multiplexer 290, and a reference signalallocator 295.

The receive path 300 in SS 116 comprises a down-converter (DC) 255, aremove cyclic prefix block 260, a serial-to-parallel (S-to-P) block 265,a Size N Fast Fourier Transform (FFT) block 270, a parallel-to-serial(P-to-S) block 275, and a channel decoding and demodulation block 280.

At least some of the components in FIGS. 2 and 3 may be implemented insoftware while other components may be implemented by configurablehardware or a mixture of software and configurable hardware. Inparticular, it is noted that the FFT blocks and the IFFT blocksdescribed in the present disclosure document may be implemented asconfigurable software algorithms, where the value of Size N may bemodified according to the implementation.

Furthermore, although the present disclosure is directed to anembodiment that implements the Fast Fourier Transform and the InverseFast Fourier Transform, this is by way of illustration only and shouldnot be construed to limit the scope of the disclosure. It will beappreciated that in an alternate embodiment of the disclosure, the FastFourier Transform functions and the Inverse Fast Fourier Transformfunctions may easily be replaced by Discrete Fourier Transform (DFT)functions and Inverse Discrete Fourier Transform (IDFT) functions,respectively. It will be appreciated that, for DFT and IDFT functions,the value of the N variable may be any integer number (i.e., 1, 2, 3, 4,etc.), while for FFT and IFFT functions, the value of the N variable maybe any integer number that is a power of two (i.e., 1, 2, 4, 8, 16,etc.).

In BS 102, channel coding and modulation block 205 receives a set ofinformation bits, applies coding (e.g., Turbo coding) and modulates(e.g., quadrature phase-shift keying (QPSK), quadrature amplitudemodulation (QAM)) the input bits to produce a sequence offrequency-domain modulation symbols. Serial-to-parallel block 210converts (i.e., de-multiplexes) the serial modulated symbols to paralleldata to produce N parallel symbol streams where N is the IFFT/FFT sizeused in BS 102 and SS 116. Size N IFFT block 215 then performs an IFFToperation on the N parallel symbol streams to produce time-domain outputsignals. Parallel-to-serial block 220 converts (i.e., multiplexes) theparallel time-domain output symbols from Size N IFFT block 215 toproduce a serial time-domain signal. Add cyclic prefix block 225 theninserts a cyclic prefix to the time-domain signal. Finally, up-converter230 modulates (i.e., up-converts) the output of add cyclic prefix block225 to radio frequency (RF) for transmission via a wireless channel. Thesignal may also be filtered at baseband before conversion to RFfrequency. In some embodiments, reference signal multiplexer 290 isoperable to multiplex the reference signals using code divisionmultiplexing (CDM) or time/frequency division multiplexing (TFDM).Reference signal allocator 295 is operable to dynamically allocatereference signals in an OFDM signal in accordance with the methods andsystem disclosed in the present disclosure.

The transmitted RF signal arrives at SS 116 after passing through thewireless channel and reverse operations performed at BS 102.Down-converter 255 down-converts the received signal to basebandfrequency and remove cyclic prefix block 260 removes the cyclic prefixto produce the serial time-domain baseband signal. Serial-to-parallelblock 265 converts the time-domain baseband signal to parallel timedomain signals. Size N FFT block 270 then performs an FFT algorithm toproduce N parallel frequency-domain signals. Parallel-to-serial block275 converts the parallel frequency-domain signals to a sequence ofmodulated data symbols. Channel decoding and demodulation block 280demodulates and then decodes the modulated symbols to recover theoriginal input data stream.

Each of base stations 101-103 may implement a transmit path that isanalogous to transmitting in the downlink to subscriber stations 111-116and may implement a receive path that is analogous to receiving in theuplink from subscriber stations 111-116. Similarly, each one ofsubscriber stations 111-116 may implement a transmit path correspondingto the architecture for transmitting in the uplink to base stations101-103 and may implement a receive path corresponding to thearchitecture for receiving in the downlink from base stations 101-103.

The total bandwidth in an OFDM system is divided into narrowbandfrequency units called subcarriers. The number of subcarriers is equalto the FFT/IFFT size N used in the system. In general, the number ofsubcarriers used for data is less than N because some subcarriers at theedge of the frequency spectrum are reserved as guard subcarriers. Ingeneral, no information is transmitted on guard subcarriers.

The transmitted signal in each downlink (DL) slot of a resource block isdescribed by a resource grid of N_(RB) ^(DL)N_(sc) ^(RB) subcarriers andN_(symb) ^(DL) OFDM symbols. The quantity N_(RB) ^(DL) depends on thedownlink transmission bandwidth configured in the cell and fulfillsN_(RB) ^(min,DL)≦N_(RB) ^(DL)≦N_(RB) ^(max,DL), where N_(RB) ^(min,DL)and N_(RB) ^(max,DL) are the smallest and largest downlink bandwidth,respectively, supported. In some embodiments, subcarriers are consideredthe smallest elements that are capable of being modulated.

In case of multi-antenna transmission, there is one resource griddefined per antenna port.

Each element in the resource grid for antenna port p is called aresource element (RE) and is uniquely identified by the index pair (k,l)in a slot where k=0, . . . , N_(RB) ^(DL)N_(sc) ^(RB)−1 and l=0, . . . ,N_(symb) ^(DL)−1 are the indices in the frequency and time domains,respectively. Resource element (k,l) on antenna port p corresponds tothe complex value a_(k,l) ^((p)). If there is no risk for confusion orno particular antenna port is specified, the index p may be dropped.

In LTE, DL reference signals (RSs) are used for two purposes. First, UEsmeasure channel quality information (CQI), rank information (RI) andprecoder matrix information (PMI) using DL RSs. Second, each UEdemodulates the DL transmission signal intended for itself using the DLRSs. In addition, DL RSs are divided into three categories:cell-specific RSs, multi-media broadcast over a single frequency network(MBSFN) RSs, and UE-specific RSs or dedicated RSs (DRSs).

Cell-specific reference signals (or common reference signals: CRSs) aretransmitted in all downlink subframes in a cell supporting non-MBSFNtransmission. If a subframe is used for transmission with MBSFN, onlythe first a few (0, 1 or 2) OFDM symbols in a subframe can be used fortransmission of cell-specific reference symbols. The notation R_(p) isused to denote a resource element used for reference signal transmissionon antenna port P.

UE-specific reference signals (or dedicated RS: DRS) are supported forsingle-antenna-port transmission on the Physical Downlink Shared Channel(PDSCH) and are transmitted on antenna port 5. The UE is informed byhigher layers whether the UE-specific reference signal is present and isa valid phase reference for PDSCH demodulation or not. UE-specificreference signals are transmitted only on the resource blocks upon whichthe corresponding PDSCH is mapped.

The time resources of an LTE system are partitioned into 10 msec frames,and each frame is further partitioned into 10 subframes of one msecduration each. A subframe is divided into two time slots, each of whichspans 0.5 msec. A subframe is partitioned in the frequency domain intomultiple resource blocks (RBs), where an RB is composed of 12subcarriers.

FIG. 4 illustrates a diagram 400 of a base station 420 in communicationwith a plurality of mobile stations 402, 404, 406, and 408 according toan embodiment of this disclosure.

As shown in FIG. 4, base station 420 simultaneously communicates withmultiple of mobile stations through the use of multiple antenna beams,each antenna beam is formed toward its intended mobile station at thesame time and same frequency. Base station 420 and mobile stations 402,404, 406, and 408 are employing multiple antennas for transmission andreception of radio wave signals. The radio wave signals can beOrthogonal Frequency Division Multiplexing (OFDM) signals.

In this embodiment, base station 420 performs simultaneous beamformingthrough a plurality of transmitters to each mobile station. Forinstance, base station 420 transmits data to mobile station 402 througha beamformed signal 410, data to mobile station 404 through a beamformedsignal 412, data to mobile station 406 through a beamformed signal 414,and data to mobile station 408 through a beamformed signal 416. In someembodiments of this disclosure, base station 420 is capable ofsimultaneously beamforming to the mobile stations 402, 404, 406, and408. In some embodiments, each beamformed signal is formed toward itsintended mobile station at the same time and the same frequency. For thepurpose of clarity, the communication from a base station to a mobilestation may also be referred to as downlink communication, and thecommunication from a mobile station to a base station may be referred toas uplink communication.

Base station 420 and mobile stations 402, 404, 406, and 408 employmultiple antennas for transmitting and receiving wireless signals. It isunderstood that the wireless signals may be radio wave signals, and thewireless signals may use any transmission scheme known to one skilled inthe art, including an Orthogonal Frequency Division Multiplexing (OFDM)transmission scheme.

Mobile stations 402, 404, 406, and 408 may be any device that is capablereceiving wireless signals. Examples of mobile stations 402, 404, 406,and 408 include, but are not limited to, a personal data or digitalassistant (PDA), laptop, mobile telephone, handheld device, or any otherdevice that is capable of receiving the beamformed transmissions.

The use of multiple transmit antennas and multiple receive antennas atboth a base station and a single mobile station to improve the capacityand reliability of a wireless communication channel is known as a SingleUser Multiple Input Multiple Output (SU-MIMO) system. A MIMO systempromises linear increase in capacity with K where K is the minimum ofnumber of transmit (M) and receive antennas (N) (i.e., K=min(M,N)). AMIMO system can be implemented with the schemes of spatial multiplexing,a transmit/receive beamforming, or transmit/receive diversity.

As an extension of SU-MIMO, multi-user MIMO (MU-MIMO) is a communicationscenario where a base station with multiple transmit antennas cansimultaneously communicate with multiple mobile stations through the useof multi-user beamforming schemes such as Spatial Division MultipleAccess (SDMA) to improve the capacity and reliability of a wirelesscommunication channel.

FIG. 5 illustrates an SDMA scheme according to an embodiment of thisdisclosure.

As shown in FIG. 5, base station 420 is equipped with 8 transmitantennas while mobile stations 402, 404, 406, and 408 are each equippedtwo antennas. In this example, base station 420 has eight transmitantennas. Each of the transmit antennas transmits one of beamformedsignals 410, 502, 504, 412, 414, 506, 416, and 508. In this example,mobile station 402 receives beamformed transmissions 410 and 502, mobilestation 404 receives beamformed transmissions 504 and 412, mobilestation 406 receives beamformed transmissions 506 and 414, and mobilestation 408 receives beamformed transmissions 508 and 416.

Since base station 420 has eight transmit antenna beams (each antennabeams one stream of data streams), eight streams of beamformed data canbe formed at base station 420. Each mobile station can potentiallyreceive up to 2 streams (beams) of data in this example. If each of themobile stations 402, 404, 406, and 408 was limited to receive only asingle stream (beam) of data, instead of multiple streamssimultaneously, this would be multi-user beamforming (i.e., MU-BF).

Downlink Control Information (DCI) format 1A is used for the compactscheduling of one PDSCH codeword and random access procedure initiatedby a Physical Downlink Control Channel (PDCCH) order.

The following information is transmitted by means of the DCI format 1A:

-   -   flag for format0/format1A differentiation—1 bit, where value 0        indicates format 0 and value 1 indicates format 1A.

Format 1A is used for a random access procedure initiated by a PDCCHorder only if the format 1A redundancy check (CRC) is scrambled with thecell radio network temporary identifier (C-RNTI) and all the remainingfields are set as follows:

-   -   localized/distributed virtual resource block (VRB) assignment        flag—1 bit is set to ‘0’;    -   resource block assignment—┌ log₂(N_(RB) ^(DL)(N_(RB)        ^(DL)+1)/2)┐ bits, where all bits are set to 1;    -   preamble index—6 bits; and—physical random access channel        (PRACH) mask index—4 bits.

All the remaining bits in format 1A for the compact schedulingassignment of one PDSCH codeword are set to zeroes. Otherwise,

-   -   localized/distributed VRB assignment flag—1 bit as defined in        section 7.1.6.3 of 3GPP TS 36.213 v8.6.0, “E-UTRA, Physical        Layer Procedures”, March 2009, which is hereby incorporated by        reference into the present application as if fully set forth        herein;    -   resource block assignment—┌ log₂(N_(RB) ^(DL)(N_(RB)        ^(DL)+1)/2)┐ bits as defined in section 7.1.6.3 of 3GPP TS        36.213 v8.6.0, “E-UTRA, Physical Layer Procedures”, March 2009:        -   for localized VRB:        -    ┌ log₂(N_(RB) ^(DL)(N_(RB) ^(DL)+1)/2)┐ bits provide the            resource allocation, and        -   for distributed VRB:        -    if N_(RB) ^(DL)<50 or if the format 1A CRC is scrambled by            RA-RNTI, paging radio network temporary identifier (P-RNTI),            or system information radio network temporary identifier            (SI-RNTI),        -    ┌ log₂(N_(RB) ^(DL)(N_(RB) ^(DL)+1)/2)┐ bits provide the            resource allocation, else        -    1 bit, the most significant bit (MSB) indicates the gap            value, where value 0 indicates N_(gap)=N_(gap,1) and value 1            indicates N_(gap)=N_(gap,2), and        -    (┌ log₂(N_(RB) ^(DL)(N_(RB) ^(DL)+1)/2)┐−1) bits provide            the resource allocation;    -   modulation and coding scheme—5 bits as defined in section 7.1.7        of 3GPP TS 36.213 v8.6.0, “E-UTRA, Physical Layer Procedures”,        March 2009, which is hereby incorporated by reference into the        present application as if fully set forth herein;    -   hybrid automatic repeat request (HARQ) process number—3 bits        (Frequency Division Duplex (FDD)), 4 bits (Time Division Duplex        (TDD));    -   new data indicator—1 bit:        -   if the format 1A CRC is scrambled by RA-RNTI, P-RNTI, or            SI-RNTI:        -   if N_(RB) ^(DL)≧50 and the localized/distributed VRB            assignment flag is set to 1, the new data indicator bit            indicates the gap value, where value 0 indicates            N_(gap)=N_(gap,1) and value 1 indicates N_(gap)=N_(gap,2),        -   else the new data indicator bit is reserved,        -   else, the new data indicator bit;    -   redundancy version—2 bits;    -   transmit power control (TPC) command for physical uplink control        channel (PUCCH)—2 bits as defined in section 5.1.2.1 of 3GPP TS        36.213 v8.6.0, “E-UTRA, Physical Layer Procedures”, March 2009,        which is hereby incorporated by reference into the present        application as if fully set forth herein,    -   if the format 1A CRC is scrambled by RA-RNTI, P-RNTI, or        SI-RNTI:    -    the most significant bit of the TPC command is reserved,    -    the least significant bit of the TPC command indicates column        N_(PRB) ^(1A) of the transport block size (TBS) table defined in        3GPP TS 36.213 v8.6.0, “E-UTRA, Physical Layer Procedures”,        March 2009, and    -    if least significant bit is 0, then N_(PRB) ^(1A)=2, else        N_(PRB) ^(1A)=3,    -   else    -    the two bits including the most significant bit indicates the        TPC command; and        -   downlink assignment index (this field is present in TDD for            all the uplink-downlink configurations and only applies to            TDD operation with uplink-downlink configuration 1-6. This            field is not present in FDD)—2 bits.

If the number of information bits in format 1A is less than that offormat 0, zeros are appended to format 1A until the payload size equalsthat of format 0.

If the number of information bits in format 1A belongs to one of thesizes in Table 5.3.3.1.2-1, one zero bit is appended to format 1A.

When the format 1A CRC is scrambled with a RA-RNTI, P-RNTI, or SI-RNTI,then the following fields among the fields above are reserved:

-   -   HARQ process number; and    -   downlink assignment index (used for TDD only and is not present        in FDD).

Compact DCI format for MU-MIMO is discussed in 3GPP R1-094350.

DCI format 1A is present for all seven transmission modes in LTE Rel-8.One purpose of DCI format 1A is to allow for a fallback operation as itis size efficient and uses transmit diversity for robust operation. Thesame principle can be used in Rel-9 for delay sum beamforming (DS-BF),although the actual transmit diversity operation needs furtherdiscussion (e.g., transparent precoding shifting or Alamouti-based). Inany case, since DCI format 1A is size-matched with DCI format 0, the newcompact DCI format should have the same size as DCI format 0.

There are two antenna ports associated with each of the new transmissionmodes. Therefore, in order to support MU-MIMO operation, a UE has to beexplicitly signalled the antenna port index. One bit is sufficient toenable such a signaling.

In DCI format 1A, there is a flag to indicate whether the assignment islocalized or distributed. For a UE-RS based beamforming operation,distributed resource allocation is of little value since UE-RS patternsare optimized for the localized assignment type. As a result, it isreasonable to re-interpret this bit as the antenna port index. Theresulting DCI format can be called DCI format 1E.

The corresponding PDSCH transmission schemes associated with DCI format1E rely on one of the new antenna ports, and are up to eNodeBimplementation. In order to support a seamless DL transmission modetransition, DCI format 1A still needs to be supported for C-RNTI. Todistinguish DCI format 1E and DCI format 1A, different CRC scramblingscan be applied.

The DCI format 2A is defined for downlink open-loop spatial multiplexingin Section 5.3.3.1.5A of 3GPP TS 36.212 v 8.6.0, “E-UTRA, Multiplexingand Channel coding”, March 2009, which is hereby incorporated byreference into the present application as if fully set forth herein.

The following information is transmitted by means of the DCI format 2A:

-   -   resource allocation header (resource allocation type 0/type 1)—1        bit as defined in section 7.1.6 of 3GPP TS 36.213 v8.6.0,        “E-UTRA, Physical Layer Procedures”, March 2009, which is hereby        incorporated by reference into the present application as if        fully set forth herein;        -   if downlink bandwidth is less than or equal to 10 physical            resource blocks (PRBs), there is no resource allocation            header and resource allocation type 0 is assumed;    -   resource block assignment:        -   for resource allocation type 0 as defined in section 7.1.6.1            of 3GPP TS 36.213 v8.6.0, “E-UTRA, Physical Layer            Procedures”, March 2009, which is hereby incorporated by            reference into the present application as if fully set forth            herein,        -    ┌N_(RB) ^(DL)/P┐ bits provide the resource allocation,        -   for resource allocation type 1 as defined in section 7.1.6.2            of 3GPP TS 36.213 v8.6.0, “E-UTRA, Physical Layer            Procedures”, March 2009, which is hereby incorporated by            reference into the present application as if fully set forth            herein,        -    ┌ log₂(P)┐ bits of this field are used as a header specific            to this resource allocation type to indicate the selected            resource blocks subset,        -    1 bit indicates a shift of the resource allocation span,            (┌N_(RB) ^(DL)/P┐−┌ log₂(P)┐−1) bits provide the resource            allocation, where the value of P depends on the number of DL            resource blocks as indicated in subclause [7.1.6.1] of 3GPP            TS 36.213 v8.6.0, “E-UTRA, Physical Layer Procedures”, March            2009, which is hereby incorporated by reference into the            present application as if fully set forth herein;    -   TPC command for PUCCH—2 bits as defined in section 5.1.2.1 of        3GPP TS 36.213 v8.6.0, “E-UTRA, Physical Layer Procedures”,        March 2009, which is hereby incorporated by reference into the        present application as if fully set forth herein;    -   downlink assignment index (this field is present in TDD for all        the uplink-downlink configurations and only applies to TDD        operation with uplink-downlink configuration 1-6. This field is        not present in FDD)—2 bits;    -   HARQ process number—3 bits (FDD), 4 bits (TDD); and    -   transport block to codeword swap flag—1 bit.

In addition, for transport block 1:

-   -   modulation and coding scheme—5 bits as defined in section 7.1.7        of 3GPP TS 36.213 v8.6.0, “E-UTRA, Physical Layer Procedures”,        March 2009, which is hereby incorporated by reference into the        present application as if fully set forth herein;    -   new data indicator—1 bit; and    -   redundancy version—2 bits.

In addition, for transport block 2:

-   -   modulation and coding scheme—5 bits as defined in section 7.1.7        of 3GPP TS 36.213 v8.6.0, “E-UTRA, Physical Layer Procedures”,        March 2009, which is hereby incorporated by reference into the        present application as if fully set forth herein;    -   new data indicator—1 bit; and    -   redundancy version—2 bits.

Precoding information—number of bits as specified in Table 5.3.3.1.5A-1.

If both transport blocks are enabled, the transport block to codewordmapping is specified according to Table 5.3.3.1.5-1.

In case one of the transport blocks is disabled, the transport block tocodeword swap flag is reserved and the transport block to codewordmapping is specified according to Table 5.3.3.1.5-2.

The precoding information field is defined according to Table5.3.3.1.5A-2. For a single enabled codeword, index 1 in Table5.3.3.1.5A-2 is only supported for retransmission of the correspondingtransport block if that transport block has previously been transmittedusing two layers with open-loop spatial multiplexing.

For transmission with 2 antenna ports, the precoding information fieldis not present. The number of transmission layers is equal to 2 if bothcodewords are enabled. Transmit diversity is used if codeword 0 isenabled while codeword 1 is disabled.

If the number of information bits in format 2A belongs to one of thesizes in Table 5.3.3.1.2-1, one zero bit is appended to format 2A.

The modulation order determination is defined for spatial multiplexingin Section 7.1.7.1 of 3GPP TS 36.213 v8.6.0, “E-UTRA, Physical LayerProcedures”, March 2009, which is hereby incorporated by reference intothe present application as if fully set forth herein.

The UE uses Q_(m)=2 if the DCI CRC is scrambled by P-RNTI, RA-RNTI, orSI-RNTI. Otherwise, the UE uses I_(MCS) and Table 7.1.7.1-1 to determinethe modulation order (Q_(m)) used in the physical downlink sharedchannel.

If the DCI CRC is scrambled by P-RNTI, RA-RNTI, or SI-RNTI, then

-   -   for DCI format 1A:    -    the UE sets the TBS index (I_(TBS)) equal to I_(MCS) and        determines its TBS by the procedure in Section 7.1.7.2.1,    -   for DCI format 1C:    -    the UE sets the TBS index (I_(TBS)) equal to I_(MCS) and        determine its TBS from Table 7.1.7.2.3-1,    -    else    -   for 0≦I_(MCS)≦28, the UE first determines the TBS index        (I_(TBS)) using I_(MBS) and Table 7.1.7.1-1 except if the        transport block is disabled in DCI formats 2 and 2A as specified        below. For a transport block that is not mapped to two-layer        spatial multiplexing, the TBS is determined by the procedure in        Section 7.1.7.2.1. For a transport block that is mapped to        two-layer spatial multiplexing, the TBS is determined by the        procedure in Section 7.1.7.2.2;    -   for 29≦I_(MCS)≦31, the TBS is assumed to be as determined from        DCI transported in the latest PDCCH for the same transport block        using 0≦I_(MCS)≦28.

In DCI formats 2 and 2A, a transport block is disabled if I_(MCS)=0 andif rvidx=1. Otherwise the transport block is enabled.

The NDI and HARQ process ID, as signalled on the PDCCH, and the TBS, asdetermined above, are delivered to higher layers.

Demodulation reference signals (DMRSs) are provided for each UE'sdemodulation. In some cases, the DMRS can be a dedicated RS (DRS) toeach UE, implying the RS provided to one UE cannot be utilized by theother UEs scheduled in different frequency bands in the same subframe,or in adjacent subframes in the same frequency band. In the case ofmulti-antenna transmissions, a number of DRSs are provided for thedemodulation of the number of multiple data streams, and each DRS issometimes precoded with the same precoder used for the data stream.

FIGS. 6A and 6B illustrate reference signal patterns according to anembodiment of this disclosure.

FIG. 6A illustrates a 2-DRS pattern 610 and FIG. 6B illustrates a 4-DRSpattern 620. Reference signal pattern 610 is an FDM/TDM pilot patternthat can support up to 2 layer transmissions. In reference pattern 610,the DRS REs are partitioned into two groups, the REs labeled with 0 andthose with 1. The DRS REs labeled with 0 carry the DRS for layer 0,while the DRS REs labeled with 1 carry the DRS for layer 1.

Reference signal pattern 620 is a CDM/FDM pilot pattern that can supportup to four layer transmissions, where DRS REs are again partitioned intotwo groups, those labeled with 0,1 and those with 2,3. For example, theDRS REs labeled with 0,1 carry the DRS for layers 0 and 1 where the twolayers' RSs are code-division multiplexed (CDMed). In the two adjacentDRS REs labeled with 0,1, a DRS symbol r0 for layer 0 is mapped to thetwo REs spread by a Walsh code [1 1] that results in [r0 r0], while aDRS symbol r1 for layer 1 is mapped to the two REs spread by a Walshcode [1-1] that results in [r1−r1].

In one embodiment, it is assumed that a first UE and a second UE arescheduled in a subframe.

In one MU-MIMO transmission mode, for the first UE, i_DRS=0 meaning thatthe first DRS pattern, DRS(0), is used for this UE.

For the second UE, i_DRS=1 meaning that the second DRS pattern, DRS(1),is used for this UE.

FIG. 7 illustrates data sections and reference signal sections of thereference pattern 610 from the perspective of two user equipmentsaccording to an embodiment of this disclosure.

FIG. 7 illustrates the behavior/observation of the first and second UEson the data section and the DRS section of the reference pattern 610. Asshown in reference signal pattern 710, the first UE only sees DRS(0) asthe pilot RE, and the other REs (other than CRS and DRS(0)) are seen bythe first UE as data REs. On the other hand, as seen in reference signalpattern 720, the second UE only sees DRS(1) as the pilot RE, and otherREs (other than CRS and DRS(1)) are seen by the second as data REs.

FIG. 8 illustrates data sections and reference signal sections of thereference pattern 610 from the perspective of two user equipmentsaccording to another embodiment of this disclosure.

In another MU-MIMO mode, for the first UE, N_DRS=2 and i_DRS=0 meaningthat the first DRS pattern, DRS(0), is used for this UE. For the secondUE, N_DRS=2 and i_DRS=1 meaning that the second DRS pattern, DRS(1), isused for this UE.

With these assumptions, FIG. 8 illustrates each UE's observation on thedata section and the DRS section of the reference pattern 610 accordingto another embodiment of this disclosure. As shown in reference signalpattern 810, the first UE only sees DRS(0) as the pilot RE, and the REs(other than CRS DRS(0), and DRS(1)) are seen by the first UE as dataREs. On the other hand, as seen in reference signal pattern 820, thesecond UE only sees DRS(1) as the pilot RE, and the REs (other than CRS,DRS(0), DRS(1)) are seen by the second UE as data REs.

Since multiple streams are transmitted by an eNodeB, each UE is toidentify its stream by a certain means. Once a UE identifies itsstreams, the UE uses dedicated reference signals (DRSs) associated withthe streams for estimating channels for the demodulation of thetransmitted streams. Here, it is assumed that the DRSs for the streamsare orthogonal to each other. For example, for demodulation of stream#0, a UE estimates channels using DRS #0 where DRS #0 is precoded withthe same precoder used to precode the data stream #0; for demodulationof stream #1, a UE estimates channels using DRS #1 where DRS #1 isprecoded with the same precoder used to precode the data stream #1.

For example, when the reference signal pattern 610 in FIG. 6A is usedfor DRS patterns, the DRS REs for DRS #0 are the RS REs labeled with 0,while the DRS REs for DRS #1 are the RS REs labeled with 1. On the otherhand, when the reference signal pattern 620 in FIG. 6B is used for DRSpatterns, the DRS #0 is multiplexed with DRS #1 in the same set of pairsof RS REs, and a Walsh code [1 1] is used for DRS #0, while a Walsh code[1-1] is used for DRS #1.

For supporting MU-MIMO, an eNodeB determines a transmission mode for UEsby higher-layer signaling. In a particular transmission mode, the eNodeBmay schedule multiple types of downlink transmissions, e.g., one fornormal transmission, another for fallback transmission, and so on. Fordifferent types of transmissions, the eNodeB transmits differentdownlink control information (DCI) formats for the downlink (DL) grants.

FIG. 9 illustrates a table 9000 summarizing downlink control information(DCI) formats used for downlink (DL) grants according to an embodimentof this disclosure.

For supporting MU-MIMO, an eNodeB may determine a transmission mode forUEs by higher-layer signaling. In a transmission mode, an eNodeB mayschedule multiple types of downlink transmissions, e.g., one for normaltransmission, another for fallback transmission, and so forth. Fordifferent types of transmissions, an eNodeB transmits different downlinkcontrol information (DCI) formats for the downlink (DL) grants.

As shown in table 900, normal transmission mode is scheduled by DCIformat 2A′, regardless of whether the transmission is configured byC-RNTI or semi-persistent scheduling (SPS) C-RNTI. In this embodiment,please note that 2A′ refers to a slightly modified version of format 2A.In normal transmission mode, a UE can receive up to two streams and upto two DRSs associated with the two streams, and an eNodeB can scheduleup to two data streams and up to two DRSs to a number of UEs in a unitof time-frequency resource. UEs in normal transmission mode are awarethat the DRS REs for the two DRSs do not carry data symbols forthemselves. On the other hand, fallback modes are scheduled by DCIformat 1A. When a DL transmission is configured by C-RNTI, the fallbacktransmission is a transmit diversity or a single-layer beamformingscheme. When a DL transmission is configured by SPS C-RNTI, the fallbacktransmission is single layer beamforming, where the DRS port index issignaled semi-statically in the upper layer other than the PHY layer. AneNodeB may schedule up to two UEs with different DRS port indicesassigned by the higher layer in the same time frequency resource bytransmitting up to two DCI format 1A to up to two UEs.

When the DRS port is assigned semi-statically, various methods may beused as described in this disclosure. For example, the UE id may beassociated with the DRS port assigned, or UEs with an even UE id wouldhave DRS port 0, while UEs with an odd UE id would have DRS port 1.

FIG. 10 illustrates a table 1000 showing a mapping of enabled codewordsto a stream index and a dedicated reference signal (DRS) index accordingto an embodiment of this disclosure.

In some embodiments of this disclosure, the stream (and the DRS) indexis indicated using an enabled codeword (CW) in a DCI format, and themapping of enabled CWs to the stream index and the DRS index can bedescribed, for example, as shown in table 1000.

As described in FIG. 4, an eNodeB may send a number of data streams to anumber of UEs, and this operation is called multi-user MIMO (MU-MIMO)operation. In one transmission mode, the eNodeB is able to transmit upto two streams in a time-frequency resource, and up to two UEs mayreceive at least one stream each in the time-frequency resource. Inanother transmission mode, the eNodeB is able to transmit up to fourstreams in a time-frequency resource, and up to four UEs may receive atleast one stream each in the time-frequency resource.

FIG. 11 illustrates a table 1100 showing a mapping of a new dataindicator (NDI) bit of a disabled codeword to a stream index and adedicated reference signal (DRS) index according to an embodiment ofthis disclosure.

As shown in FIG. 11, the stream (and the DRS) index is indicated usingan NDI bit for a disabled CW in a DCI format, and the mapping of the NDIbit of a disabled CW to the stream index and the DRS index can bedescribed, for example, as shown in table 1100.

Several scrambling sequence generation and mapping methods have beenproposed for multi-layer beamforming. The initialization of the RSsequence can be cell-specific, UE specific, and/or antenna-portspecific. When the initialization of the DRS sequence is cell-specific[UE specific, antenna-port specific], the initialization seed can bedetermined as a function of the cell-id [UE id or RNTI, antenna portnumber].

FIG. 12 illustrates a system 1200 for generating and mapping referencesignal sequences according to an embodiment of this disclosure.

As shown in FIG. 12, system 1200 generates a plurality of RS sequencesand maps the generated RS sequences onto a number of antenna ports intwo steps. The generated RS sequences can be mapped onto eithercell-specific antenna ports or UE-specific (or dedicated) antenna ports.

The RS sequence generator 1201 receives an initialization seedc_(init,g) for generating a pseudo-random sequence c_(g)(i). The RSsequence generator 1201 then uses the pseudo-random sequence c_(g)(i) togenerate a respective RS sequence for each of the antenna ports andsends each RS sequence to a respective resource element mapper 1203-1 to1203-n for each of the antenna ports.

Demodulation reference signals (DMRSs) are provided for each UE'sdemodulation. In some cases, the DMRS can be a dedicated RS (DRS) toeach UE, implying that the RS provided to one UE cannot be utilized bythe other UEs scheduled in different frequency bands in the samesubframe, or in adjacent subframes in the same frequency band. In thecase of multi-antenna transmissions, a number of DRSs are provided forthe demodulation of the number of multiple data streams, and each DRS issometimes precoded with the same precoder used for data stream.

When multiple UEs are co-scheduled in the same frequency band, a firstnumber of streams are transmitted to a first UE, and a second number ofstreams are transmitted to a second UE. The present disclosure providestwo possible ways for the eNodeB to provide each UE's DRS in thismulti-user MIMO transmission.

In one embodiment referred to as non-transparent MU-MIMO, the eNodeBprovides orthogonal sets of DRS to the UEs, where the first and thesecond UEs receive the first and the second number of orthogonal DRSs.All of the first number and the second number of DRSs are orthogonallymultiplexed, e.g., by FDM/TDM or CDM. Furthermore, the first UE and thesecond UE know that there could be other UEs co-scheduled in the sametime-frequency resource.

In another embodiment referred to as transparent MU-MIMO or SU-MIMO, theeNodeB provides the first and the second number of DRSs to the first andthe second UEs. In this method, the first number and the second numberof DRSs may not be orthogonally multiplexed. Furthermore, the first andthe second UEs may not be able to know that there could be other UEsco-scheduled in the same time-frequency resource.

In one example, two UEs, UE 0 and UE 1, are co-scheduled in the samefrequency band by an eNodeB, where UE 0 would receive stream 0, while UE1 would receive stream 1.

When non-transparent MU-MIMO is used, UE 0 would receive DRS 0 togetherwith stream 0, while UE 1 would receive DRS 1 together with stream 1.FIGS. 6A and 6B illustrate specific DRS patterns with FDM/TDM and withCDM that may be used. For example, in the FDM pattern shown in thereference signal pattern 610, UE 0 would receive its DRS in the RS REswith label 0, while UE 1 would receive its DRS in the RS REs with label1. If UE 0 knows that another UE is co-scheduled in the time-frequencyresource where it receives the downlink transmission by certain means,UE 0 may try to estimate interfering channels in the other DRS REs,i.e., the RS REs with label 1, and use the interference information fordemodulation.

When transparent MU-MIMO is used, UE 0 and UE 1's DRSs are notnecessarily orthogonally multiplexed, and each UE assumes that there areno co-scheduled UEs in the time-frequency resource where it receives thedownlink transmission. In other words, in this MU-MIMO mode, the UEsexpect SU-MIMO transmissions from the eNodeB. In one example, both UE 0and UE 1 would receive DRS in the same set of RS REs, e.g., RS REs withlabel 0 in FIG. 6A or 6B.

For single-user transmissions in a time-frequency resource of aneNodeB's cell, RS scrambling has been used to make the inter-cellinterference independent of the desired RS signal to a UE. In eachdownlink transmission, a UE receives a distorted RS signal that is asuperposition of the desired RS signal, the interfering RS signal fromother cells, and the noise. With a cell-specific RS scrambling sequence,the inter-cell interference seen at a UE becomes independent of thedesired RS signal, which facilitates the channel estimation.

In the case of multi-user transmissions, more considerations with regardto DRS scrambling to facilitate the channel and the intra-cellinterference estimations are needed. There are two ways to perform DRSscrambling. In a first method, DRS 0 and DRS 1 are scrambled in aUE-specific way. In a second method, DRS 0 and DRS 1 are scrambled in acell-specific way, as for single-user transmissions.

With regard to the first method, when non-transparent MU-MIMO is used,two UEs have two orthogonal sets of resources (DRS REs) for the two setsof DRSs. In this case, even if UE 1 knows of the RS REs for the UE 0'sDRS, UE 1 may not be aware of the scrambling sequence used for the DRSfor UE 0's stream since UE 1 does not know the UE id for UE 0. In such acase, UE 1 may not be able to estimate the interfering channels. On theother hand, when transparent MU-MIMO is used, two UEs may receive theirDRSs in the same set of DRS REs. In the set of DRS REs, UE 1 wouldreceive a distorted RS signal that is a superposition of the desired RSsignal, the interfering RS signal intended for UE 1, and the noise. Whenthe scrambling sequence is UE-specific, the interfering RS signal isindependent of the desired RS signal to UE 1, which enables UE 1 tomeasure its channel separately from the interfering channel intended forUE 0.

In the case where DRSs are scrambled using the second scrambling methodand non-transparent MU-MIMO is used, two UEs would have two orthogonalsets of resources (DRS REs) for the two sets of DRSs. In this case, ifUE 1 knows the RS REs for the UE 0's DRS, UE 1 would be aware of thescrambling sequence used for the DRS for UE 0's stream since the DRS iscell-specific. In such a case, UE 1 may be able to estimate theinterfering channels carried in the DRS REs with label 0.

On the other hand, when transparent MU-MIMO is used, two UEs may receivetheir DRSs in the same set of DRS REs. In the set of DRS REs, UE 1 wouldreceive a distorted RS signal that is a superposition of the desired RSsignal, the interfering RS signal intended for UE 1, and the noise. Whenthe scrambling sequence is cell-specific, the interfering RS signal isaligned with the desired RS signal to UE 1. In such a case, UE 1 canonly measure the superimposed channel of the interfering channel and thedesired channel, which could degrade the demodulation performance.

Accordingly, one scrambling method cannot universally give good channelestimation and demodulation performance in both scenarios of MU-MIMO.Accordingly, this disclosure provides a method and system to adapt thescrambling method according to the MU-MIMO modes in a wirelesscommunication system.

In some embodiments, the UE-specific scrambling method has aninitialization seed for each DRS, and the initialization seed isdependent on the UE-id or RNTI number. The initialization seed may ormay not be dependent on the antenna port id or the cell-id.

In one particular embodiment, the initialization seed is determinedusing Equation 1 below:c _(init)=(└n _(s)/2┘+1)·(2N _(ID) ^(cell)+1)·2¹⁶ +n _(RNTI),  [Eqn. 1]where n_(s) is the slot id, N_(ID) ^(cell) is the cell id, and n_(RNTI)is the UE-id or the radio network temporary identifier (RNTI) number. Inanother particular embodiment, the initialization seed is determinedusing Equation 2 below:c _(init)=(g+z+1)(└n _(s)/2┘+1)·(2N _(ID) ^(cell)+1)·2¹⁶ +n_(RNTI),  [Eqn. 2]where g is an antenna port number (e.g., 0 or 1 when there are twoantenna ports) and z is an integer (e.g., 0 or 1).

In yet another particular embodiment, the initialization seed isdetermined using Equation 3 below:c _(init)=(└n _(s)/2┘+g+z+1)·(2N _(ID) ^(cell)+1)·2¹⁶ +n _(RNTI),  [Eqn.3]where g is an antenna port number.

In other embodiments, the cell-specific scrambling method has aninitialization seed for each DRS, and the initialization seed isdependent on the cell-id. The initialization seed may or may not bedependent on the antenna port id and is not dependent the UE-id or RNTI.

In a particular embodiment, the initialization seed is determined usingEquation 4 below:c _(init)=(└n _(s)/2┘+1)·(2N _(ID) ^(cell)+1)·2¹⁶,  [Eqn. 4]where n_(s) is the slot id, N_(ID) ^(cell) is the cell id, and n_(RNTI)is the UE-id or the RNTI number.

In another particular embodiment, the initialization seed is determinedusing Equation 5 below:c _(init)=(g+1)(└n _(s)/2┘+1)·(2N _(ID) ^(cell)+1)·2¹⁶,  [Eqn. 5]where g is an antenna port number, e.g., 0 or 1 when there are twoantenna ports.

In yet another particular embodiment, the initialization seed isdetermined using Equation 6 below:c _(init)=(└n _(s)/2┘+g+1)·(2N _(ID) ^(cell)+1)·2¹⁶,  [Eqn. 6]where g is an antenna port number.

Once the scrambling sequence is initialized, the scrambling sequencesare generated, for example, according to the methods and systemsdescribed in U.S. Non-provisional patent application Ser. No.12/749,340, filed Mar. 29, 2010, entitled “METHOD AND SYSTEM FORMULTI-LAYER BEAMFORMING”, which is hereby incorporated by reference intothe present application as if fully set forth herein.

FIG. 13 illustrates a method 1300 of operating an eNodeB or base stationaccording to an embodiment of this disclosure.

As shown in FIG. 13, method 1300 includes sending a DL grant to ascheduled UE or mobile station. The DL grant conveys information on theDRS scrambling method (block 1301). Method 1300 also includestransmitting data streams along with corresponding DRSs scrambled withthe scrambling method specified in the DL grant (block 1303).

FIG. 14 illustrates a method 1400 of operating a UE or mobile stationaccording to an embodiment of this disclosure.

As shown in FIG. 14, method 1400 includes receiving a DL grant from aneNodeB or base station. The DL grant conveys information on the DRSscrambling method (block 1401). Method 1400 also includes receiving datastreams along with corresponding DRSs scrambled with the scramblingmethod specified in the DL grant (block 1403). Method 1400 furtherincludes de-scrambling the DRSs according to the scrambling methodspecified in the DL grant (block 1405).

FIG. 15 illustrates a table 1500 depicting two states in a downlink (DL)grant according to an embodiment of this disclosure.

As shown in table 1500, the two choices are indicated in the DL grant astwo states, where the first state indicates cell-specific scrambling ofthe DRS sequence and the second state indicates UE-specific scramblingof the DRS sequence.

There are many ways to construct two codepoints in the DL grant torepresent these two states. In one embodiment, a one-bit field is addedto the DL grant, and this one-bit field is used to indicate these twostates. This embodiment applies to any DCI format that an eNodeB uses tosend the DL grant to a UE.

FIG. 16 illustrates a table 1600 depicting two states in a downlink (DL)grant using a one-bit field according to an embodiment of thisdisclosure.

In this particular embodiment, a first value of “0” in the one-bit fieldindicates the first state in which cell-specific scrambling of the DRSsequence is used. A second value of “1” in the one-bit field indicatesthe second state in which UE-specific scrambling of the DRS sequence isused.

In an embodiment of this disclosure, the number of enabled TBs (1 or 2)in the DL grant is used to indicate the choice of cell-specificscrambling or UE-specific scrambling. This embodiment is applicable forthe DCI formats that can indicate two TBs, for example, the 2A′ DCIformat mentioned above (which is based on 2A). For the case when the DCIformat only supports 1 TB, then the choice of scrambling method isdependent on the transmission scheme. For example, if transmit diversityis used, then UE-specific scrambling is adopted. If single-DRS portscheme is used, cell-specific scrambling is adopted.

FIG. 17 illustrates a table 1700 summarizing the indication of the DRSscrambling method as a function of the DCI format, the number of enabledTBs and the transmission mode according to an embodiment of thisdisclosure.

DCI format 1A′ in table 1700 refers to a slightly modified version offormat 1A. Although Rel-8 currently only allows the combination ofC-RNTI with transmit diversity, and SPS-RNTI with single DRS-porttransmission scheme, in Rel-9 and beyond, the other two combinations(C-RNTI with single DRS-port, and SPS-RNTI with transmit diversity) mayalso be possible. For the case of DCI format 2A or 2A′, the embodimentsof this disclosure may be combined with any number of methods forindicating the DRS port index. For the case of DCI format 1A or 1A′, theembodiments of this disclosure can be combined with semi-staticindication of the DRS port index, such as radio resource control (RRC)signaling, or fixed indication of the DRS port index, such asassociation of the DRS port index with the UE ID, etc.

FIG. 18 illustrates a table 1800 depicting two states in a downlink (DL)grant according to another embodiment of this disclosure.

In an embodiment of this disclosure, the choice of the DRS scramblingmethod is indicated by the eNodeB to the UE by the downlink grant asshown in FIG. 13. The two choices are indicated in the DL grant as oneof two state as shown in table 1800, where the first state indicatesgroup-specific scrambling of the DRS sequence and the second stateindicates UE-specific scrambling of the DRS sequence. The group-specificscrambling is very similar to cell-specific scrambling, except that thecell-id is replace by the group id (which indicates which group the UEbelongs to, where the UEs in a particular cell are divided into severalgroups) in the initialization step of scrambling. The group id iscommunicated to the user by either higher-layer UE-specific RRCsignaling or secondary broadcast system information block (SIB)signaling.

In one example, the initialization seed is determined using Equation 7below:c _(init)=(└n _(s)/2┘+1)·(2N _(ID) ^(group)+1)·2¹⁶,  [Eqn. 7]where n_(s) is the slot id, N_(ID) ^(group) is the group id, andn_(RNTI) is the UE-id or the RNTI number.

FIG. 19 illustrates a table 1900 depicting two states in a downlink (DL)grant using a one-bit field according to another embodiment of thisdisclosure.

There are many ways to construct two codepoints in the DL grant torepresent these two states. One codepoint construction method includesadding a one-bit field to the DL grant, and using this one-bit field toindicate these two states. This method applies to any DCI format that aneNodeB uses to send a DL grant to a UE. A particular embodiment of thismethod is illustrated in table 1900.

FIG. 20 illustrates a table 2000 summarizing the indication of the DRSscrambling method as a function of the DCI format, the number of enabledTBs and the transmission mode according to another embodiment of thisdisclosure.

In an embodiment of this disclosure, the number of enabled TBs (1 or 2)in the DL grant is used to indicate the choice of either group-specificscrambling or UE-specific scrambling. This is applicable for the DCIformats that can indicate two TBs, for example, the 2A′ DCI formatmentioned above (which is based on 2A). For the case where the DCIformat only supports 1 TB, the choice of scrambling method is dependenton the transmission scheme. For example, if transmit diversity is used,then UE-specific scrambling is adopted. If a single-DRS port scheme isused, then group-specific scrambling is adopted.

DCI format 1A′ in table 2000 refers to a slightly modified version offormat 1A. Although Rel-8 currently only allows the combination ofC-RNTI with transmit diversity, and SPS-RNTI with single DRS-porttransmission scheme, in Rel-9 and beyond, the other two combinations(C-RNTI with single DRS-port, and SPS-RNTI with transmit diversity) mayalso be possible. For the case of DCI format 2A or 2A′, the embodimentsof this disclosure may be combined with any number of methods forindicating the DRS port index. For the case of DCI format 1A or 1A′, theembodiments of this disclosure can be combined with semi-staticindication of the DRS port index, such as RRC signaling, or fixedindication of the DRS port index, such as association of the DRS portindex with the UE ID, etc.

FIG. 21 illustrates a table 2100 depicting use of an existing bit in aparticular downlink (DL) grant to indicate the choice of cell-specificscrambling or UE-specific scrambling according to an embodiment of thisdisclosure.

In one embodiment of this disclosure, an existing bit in a particular DLgrant is reinterpreted to indicate these two states. This embodimentalso is applicable for DCI formats that can indicate two TBs, forexample, the 2A′ DCI format mentioned above (which is based on 2A). Thisembodiment involves the following:

-   -   if both TB1 and TB2 are enabled, then UE-specific scrambling is        always used (to allow transparent MU-MIMO);    -   if one of the TBs is disabled, then the codepoints needed to        represent the two states (of the scrambling method) are obtained        by reinterpreting either the NDI bit of the disabled TB or the        TB to CW mapping bit (which is similar to using the two        codepoints (states) of the enabled CW index (as show in table        1000)); and    -   if one of the TB is disabled, the same set of codepoints can        also be used to indicate whether the UE should expect total rank        of 1 (SU-MIMO) or 2 (MU-MIMO with each user sending rank-1).        In addition, the treatment is the same as in the above        embodiment, for the case where the UE receives a DCI format that        supports only 1 TB.

This embodiment in summarized in table 2100. As mentioned above, the bitto be reinterpreted could be the NDI bit of the disabled TB, the CW toTB mapping bit, or the two states associated with which CW is enabled.

Again, in this embodiment for the case of DCI format 2A or 2A′, theembodiments of this disclosure may be combined with any number ofmethods for indicating the DRS port index. For the case of DCI format 1Aor 1A′, the embodiments of this disclosure can be combined withsemi-static indication of the DRS port index, such as RRC signaling, orfixed indication of the DRS port index, such as association of the DRSport index with the UE ID, etc.

In another embodiment of this disclosure, the state of the DRSscrambling method is carried semi-statically in higher layer signaling,e.g., RRC signaling.

In one example, the eNodeB signals the first scrambling method to a UEwhen the eNodeB intends to use non-transparent MU-MIMO for the UE, andthe eNodeB signals the second scrambling method to a UE when the eNodeBintends to use transparent MU-MIMO for the UE.

FIG. 22 illustrates a method 2200 of operating an eNodeB or base stationaccording to another embodiment of this disclosure.

As shown in FIG. 22, method 2200 includes transmitting an RRC message toa scheduled UE or mobile station. The RRC message conveys information onthe DRS scrambling method (block 2201). Method 1300 also includestransmitting a DL grant to the scheduled UE or mobile station (block2203). Method 1300 further includes transmitting data streams along withcorresponding DRSs scrambled with the scrambling method specified in RRCmessage (block 2205).

FIG. 23 illustrates a method 2300 of operating a UE or mobile stationaccording to an embodiment of this disclosure.

As shown in FIG. 23, method 2300 includes receiving an RRC message froman eNodeB or base station. The RRC message conveys information on theDRS scrambling method (block 2301). Method 2300 also includes receivinga DL grant from the eNodeB or base station (block 2303). Method 2300further includes receiving data streams along with corresponding DRSsscrambled with the scrambling method specified in the RRC message (block2305). Method 2300 further includes de-scrambling the DRSs according tothe scrambling method specified in the RRC message (block 2307).

In another embodiment of this disclosure, the state of the DRSscrambling method is conveyed by the DCI format used for the downlinkgrant.

For example, for UEs in transmission mode A as summarized in table 900,two DCI formats can be transmitted, DCI format 2A and DCI format 1A. Ina particular embodiment, DCI format 1A is associated with the first DRSscrambling method, and DCI format 2A is associated with the second DRSscrambling. In this case, when DCI format 1A is transmitted as adownlink grant, the eNodeB scrambles the scrambling sequence using thefirst DRS scrambling method 1. When DCI format 2A is transmitted as adownlink grant, the eNodeB scrambles the scrambling sequence using thesecond DRS scrambling method. Of course, another possible way is toassociate DCI format 1A with the second DRS scrambling method and DCIformat 2A with the first DRS scrambling method.

FIG. 24 illustrates a method 2400 of operating an eNodeB or base stationaccording to a further embodiment of this disclosure.

As shown in FIG. 24, method 2400 includes determining whether a firstscrambling method or a second scrambling method is to be used for aparticular UE or mobile station (block 2401). If the first scramblingmethod is to be used, method 2400 also includes transmitting a DL grantto the scheduled UE or mobile station using DCI format 1A (block 2403),and transmitting data streams along with corresponding DRSs scrambledwith the first scrambling method (block 2405). If the second scramblingmethod is to be used, method 2400 also includes transmitting a DL grantto the scheduled UE or mobile station using DCI format 2A (block 2407),and transmitting data streams along with corresponding DRSs scrambledwith the second scrambling method (block 2409).

FIG. 25 illustrates a method 2500 of operating a UE or mobile stationaccording to an embodiment of this disclosure.

As shown in FIG. 25, method 2500 includes receiving a DL from the eNodeBor base station (block 2501). Method 2500 also includes determiningwhether DCI format 1A or 2A is received (block 2503). If DCI format 1Ais received, method 2500 further includes receiving data streams alongwith corresponding DRSs scrambled with a first scrambling method (block2505), and de-scrambling the DRSs according to the first scramblingmethod (block 2507). If DCI format 2A is received, method 2500 furtherincludes receiving data streams along with corresponding DRSs scrambledwith a second scrambling method (block 2509), and de-scrambling the DRSsaccording to the second scrambling method (block 2511).

Demodulation reference signals (DMRSs) are provided for each UE'sdemodulation. In some cases, the DMRS can be a dedicated RS (DRS) toeach UE, implying the RS provided to one UE cannot be utilized by theother UEs scheduled in different frequency bands in the same subframe,or in adjacent subframes in the same frequency band. In the case ofmulti-antenna transmissions, a number of DRSs are provided for thedemodulation of the number of multiple data streams, and each DRS can beprecoded with the same precoder used for data stream.

From one of UE-specific RRC signaling, UE-specific dynamic signaling andbroadcast signaling, UEs receive cell-id N_(ID) ^(cell) and group-idN_(ID) ^(group) from an eNodeB. Here, the group id indicates the groupof UEs to which a particular UE belongs. There can be several ways inwhich a group formed. For example, for a single-cell operation, a groupis formed by a subset of UEs in a cell. For a coordinated multi-point(COMP) operation, a group is formed by a subset of UEs from severalcells within the COMP measurement area.

The time slots are indexed by a slot number n_(S), and a UE is aware ofthe slot number in each slot where the UE receives downlink signals, andwhere the UE transmits uplink signals.

In a subframe composed of two time slots, the eNodeB assigns a number ofdownlink resource blocks (RBs) to a UE, and transmits data streams andthe DM RS in the assigned RBs, where one DM RS is transmitted per datasteam, to the UE. The DM RS sequence for each stream can be generated,for example, following the procedure in 3GPP TS 36.211 v 8.6.0, “E-UTRA,Physical channels and modulation”, March 2009, with an initializationseed of pseudo-random sequence generated from at least one of a cell-id,a group id and a slot number in a subframe. 3GPP TS 36.211 v 8.6.0,“E-UTRA, Physical channels and modulation”, March 2009, is herebyincorporated by reference into the present application as if fully setforth herein.

In one embodiment of this disclosure, the initialization seed isdetermined using Equation 8 below:c _(init)=(└n _(s)/2┘+1)·(2N _(ID) ^(cell)+1)·(AN _(ID) ^(group)+1)2^(B)+C,  [Eqn. 8]where n_(s) is the first slot number in the subframe, N_(ID) ^(cell) isthe cell id, N_(ID) ^(group) is the group id, and A, B, C are integers.For example, A is either 1 or 2, B is an integer less than or equal to16, and C is an integer less than 2^(B).

In another embodiment of this disclosure, the initialization seed isdetermined using Equation 9 below:c _(init)=(└n _(s)/2┘+1)·(2N _(ID) ^(cell) +AN _(ID) ^(group)+1)·2^(B)+C,  [Eqn. 9]where n_(s) is the first slot number in the subframe, N_(ID) ^(cell) isthe cell id, N_(ID) ^(group) is the group id, and A, B, C are integers.For example, A is either 1 or 2, B is an integer less than or equal to16, and C is an integer less than 2^(B).In a further embodiment of this disclosure, the initialization seed isdetermined using Equation 10 below:c _(init)=(└n _(s)/2┘+1)·(2N _(ID) ^(cell)+1)·2^(B) N _(ID)^(group),  [Eqn. 10]where n_(s) is the first slot number in the subframe, N_(ID) ^(cell) isthe cell id, N_(ID) ^(group) is the group id, and B is an integer. Forexample, B is an integer less than or equal to 16, and N_(ID) ^(group)is an integer less than 2^(B).

In one embodiment of the current disclosure, a one-bit group id, i.e.,either 0 or 1, is dynamically indicated to a UE via a codepoint in a DLgrant sent by the eNodeB.

When format 2B is used for the DL grant, at least one of the followingcodepoints has been defined in format 2A for use as a one-bit group idindication: the transport block to codeword (TB-to-CW) swap bit and theNDI bit of a disabled TB. One of the other codepoints that is not usedfor the one-bit group id indication can be used for stream indexindication.

FIG. 26 illustrates a table 2600 summarizing a method of indicating agroup id and a stream index using the DCI format 2B according to anembodiment of this disclosure.

As shown in table 2600, in an embodiment of this disclosure, theTB-to-CW swap bit carries the one-bit group id, and the NDI bit of thedisabled TB is used for indicating the stream index.

FIG. 27 illustrates a table 2700 summarizing a method of indicating agroup id and a stream index using the DCI format 2B according to anotherembodiment of this disclosure.

As shown in table 2700, in an embodiment of this disclosure, theTB-to-CW swap bit carries the stream index, and the NDI bit of thedisabled TB is used for indicating the group id.

FIG. 28 illustrates a table 2800 summarizing a method of indicating agroup id and a stream index using the DCI format 1E according to anembodiment of this disclosure.

When format 1E is used for DL grant, at least one of the followingcodepoints has been defined in format 1A for use as a one-bit group idindication: localized/distributed VRB assignment flag, flag forformat0/format1A differentiation, and the most significant bit of theTPC command for PUCCH. One of the other codepoints that is not used forthe one-bit group id indication can be used for stream index indication.

As shown in table 2800, in an embodiment of this disclosure, thelocalized/distributed VRB assignment flag bit carries the one-bit groupid, and the most significant bit of the TPC command is used forindicating the stream index.

FIG. 29 illustrates a table 2900 summarizing a method of indicating agroup id and a stream index using the DCI format 1E according to anotherembodiment of this disclosure.

As shown in table 2900, in an embodiment of this disclosure, the mostsignificant bit of the TPC command carries the one-bit group id, and thelocalized/distributed VRB assignment flag bit is used for indicating thestream index.

FIG. 30 illustrates a linkage between a location of a control channelelement (CCE) aggregation and a group id according to an embodiment ofthis disclosure.

In an embodiment of this disclosure, the group id is dynamicallyindicated to a UE by at least one of the following information relatedto a DL grant available to both the UE and the eNodeB: CCE indices thatcarry the DL grant, the UE id number, and the relative position of theCCEs that carry the DL grant in the tree diagram. In this embodiment,the DL grant can be any of the DCI formats used as DL grants within atransmission mode, including at least format 1E and format 2B.

In one example, one of the CCE indices that carry a DL grant for a UEdetermines the group id of the UE. In another example, if the smallestCCE index that carries a DL grant is even, group id 0 is indicated.Otherwise, group id 1 is indicated. In a further example, if CCEscarrying a DL grant are in the left hand side of the CCE tree, group id0 is indicated. If CCEs carrying the DL grant are in the right hand sideof the CCE tree, group id 1 is indicated.

In another example, if a UE id is even, group id 0 is indicated.Otherwise, group id 1 is indicated.

In another embodiment of this disclosure, the group id issemi-statically indicated to a UE by at least one of the following ofhigher layer signaling methods: UE-specific RRC signaling and broadcastsignaling.

FIG. 31 illustrates a method 3100 of operating an eNodeB or base stationaccording to yet another embodiment of this disclosure.

Method 3100 includes transmitting a downlink grant to a scheduled UE ormobile station (block 3103). Method 3100 also includes generating areference signal sequence for a reference signal for two or more antennaports using one initialization seed c_(init) defined as follows:c _(init)=(└n _(s)/2┘+1)·(2N _(ID) ^(cell)+1)·2¹⁶ +N _(ID) ^(group),where n_(s) is a first slot number in a subframe, N_(ID) ^(cell) is acell identifier of the base station, and N_(ID) ^(group) is a group(block 3103). In a particular embodiment, the N_(ID) ^(group) is aone-bit group identifier dynamically indicated in a codepoint in thedownlink grant. Method 3100 further includes transmitting the referencesignal (block 3105).

FIG. 32 illustrates a method 3200 of operating a UE or mobile stationaccording to yet another embodiment of this disclosure.

Method 3200 includes receiving a downlink grant from a base station(3201), and receiving a reference signal generated at the base stationusing one initialization seed defined as follows:c _(init)=(└n _(s)/2┘+1)·(2N _(ID) ^(cell)+1)·2¹⁶ +N _(ID) ^(group),where n_(s) is a first slot number in a subframe, N_(ID) ^(cell) is acell identifier of the base station, and N_(ID) ^(group) is a groupidentifier (block 3203). In a particular embodiment, the N_(ID) ^(group)is a one-bit group identifier dynamically indicated in a codepoint inthe downlink grant.

Although the present disclosure has been described with an exemplaryembodiment, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present disclosure encompasssuch changes and modifications as fall within the scope of the appendedclaims.

What is claimed is:
 1. A base station, comprising: a reference signalsequence generator configured to generate a reference signal sequencefor a reference signal for each of n antenna ports using oneinitialization seed c_(init), n being a positive integer, wherein theinitialization seed is defined as:c _(init)=(└n _(s)/2┘+1)·(2N _(ID) ^(cell)+1)·2¹⁶ +N _(ID) ^(group),where n_(s) is a slot number in a subframe, N_(ID) ^(cell) is a cellidentifier of the base station, and N_(ID) ^(group) is a groupidentifier; and a transmit path circuitry configured to transmit adownlink grant and the reference signal.
 2. The base station inaccordance with claim 1, wherein the Group identifier N_(ID) ^(group) isa one-bit group identifier dynamically indicated in a codepoint in thedownlink grant transmitted by the base station.
 3. The base station inaccordance with claim 2, wherein the codepoint indicating the one-bitgroup identifier N_(ID) ^(group) is one of the following codepointsdefined in (DCI) format 2A: a transport block to codeword (TB-to-CW)swap bit and a new data indicator (NDI) bit of a disabled transportblock (TB), and wherein the other of the codepoints defined in DCIformat 2A that is not used to indicate the one-bit group identifierN_(ID) ^(group) is used to indicate a stream index.
 4. The base stationin accordance with claim 2, wherein the one-bit group identifier N_(ID)^(group) is indicated by a transport block to codeword (TB-to-CW) swapbit defined in DCI format 2A, and a stream index is indicated by a newdata indicator (NDI) bit of a disabled transport block (TB) defined inDCI format 2A.
 5. The base station in accordance with claim 2, whereinthe one-bit group identifier N_(ID) ^(group) and a stream index areindicated by a transport block to codeword (TB-to-CW) swap bit and a newdata indicator (NDI) bit of a disabled transport block (TB) defined inDCI format 2A as follows: Reinterpreted Reinterpreted NDI bit ofTB-to-CW swap bit the disabled TB (group id, stream id) 0 0 (0, 0) 0 1(0, 1) 1 0 (1, 0) 1 1 (1, 1).


6. A method of operating a base station, the method comprising:generating, at a reference signal sequence generator, a reference signalsequence for a reference signal for each of n antenna ports using oneinitialization seed c_(init), n being a positive integer, wherein theinitialization seed is defined as:c _(init)=(└n _(s)/2┘+1)·(2N _(ID) ^(cell)+1)·2¹⁶ +N _(ID) ^(group),where n_(s) is a first slot number in a subframe, N_(ID) ^(cell) is acell identifier of the base station, and N_(ID) ^(group) is a groupidentifier; and transmitting a downlink grant and the reference signal.7. The method in accordance with claim 6, wherein the group identifierN_(ID) ^(group) is a one-bit group identifier dynamically indicated in acodepoint in the downlink grant transmitted by the base station.
 8. Themethod in accordance with claim 7, wherein the codepoint indicating theone-bit group identifier N_(ID) ^(group) is one of the followingcodepoints defined in DCI format 2A: a transport block to codeword(TB-to-CW) swap bit and a new data indicator (NDI) bit of a disabledtransport block (TB), and wherein the other of the two above codepointsdefined in DCI format 2A that is not used to indicate the one-bit groupidentifier N_(ID) ^(group) is used to indicate a stream index.
 9. Themethod in accordance with claim 7, wherein the one-bit group identifierN_(ID) ^(group) is indicated by a transport block to codeword (TB-to-CW)swap bit defined in DCI format 2A, and a stream index is indicated by anew data indicator (NDI) bit of a disabled transport block (TB) definedin DCI format 2A.
 10. The method in accordance with claim 7, wherein theone-bit group identifier N_(ID) ^(group) and a stream index areindicated by a transport block to codeword (TB-to-CW) swap bit and a newdata indicator (NDI) bit of a disabled transport block (TB) defined inDCI format 2A as follows: Reinterpreted Reinterpreted NDI bit ofTB-to-CW swap bit the disabled TB (group id, stream id) 0 0 (0, 0) 0 1(0, 1) 1 0 (1, 0) 1 1 (1, 1).


11. A subscriber station, comprising: a receive path circuitryconfigured to: receive a downlink grant from a base station; and receivea reference signal generated at the base station using oneinitialization seed c_(init), wherein the initialization seed is definedas:c _(init)=(└n _(s)/2┘+1)·(2N _(ID) ^(cell)+1)·2¹⁶ +N _(ID) ^(group),where n_(s) is a first slot number in a subframe, N_(ID) ^(cell) is acell identifier of the base station, and N_(ID) ^(group) is a groupidentifier.
 12. The subscriber station in accordance with claim 11,wherein the group identifier N_(ID) ^(group) is a one-bit groupidentifier dynamically indicated in a codepoint in the downlink grant.13. The subscriber station in accordance with claim 12, wherein thecodepoint indicating the one-bit group identifier N_(ID) ^(group) is oneof the following codepoints defined in DCI format 2A: a transport blockto codeword (TB-to-CW) swap bit, and a new data indicator (NDI) bit of adisabled transport block (TB), and wherein the other of the codepointsdefined in DCI format 2A that is not used to indicate the one-bit groupidentifier N_(ID) ^(group) is used to indicate a stream index.
 14. Thesubscriber station in accordance with claim 12, wherein the one-bitgroup identifier N_(ID) ^(group) is indicated by a transport block tocodeword (TB-to-CW) swap bit defined in DCI format 2A, and a streamindex is indicated by a new data indicator (NDI) bit of a disabledtransport block (TB) defined in DCI format 2A.
 15. The subscriberstation in accordance with claim 12, wherein the one-bit groupidentifier N_(ID) ^(group) and a stream index are indicated by atransport block to codeword (TB-to-CW) swap bit and a new data indicator(NDI) bit of a disabled transport block (TB) defined in DCI format 2A asfollows: Reinterpreted Reinterpreted NDI bit of TB-to-CW swap bit thedisabled TB (group id, stream id) 0 0 (0, 0) 0 1 (0, 1) 1 0 (1, 0) 1 1(1, 1).


16. A method of operating a subscriber station, the method comprising:receiving a downlink grant from a base station; and receiving areference signal generated at the base station using one initializationseed c_(init), wherein the initialization seed is defined as:c _(init)=(└n _(s)/2┘+1)·(2N _(ID) ^(cell)+1)·2¹⁶ +N _(ID) ^(group),where n_(s) is a first slot number in a subframe, N_(ID) ^(cell) is acell identifier of the base station, and N_(ID) ^(group) is a groupidentifier.
 17. The method in accordance with claim 16, wherein thegroup identifier N_(ID) ^(group) is a one-bit group identifierdynamically indicated in a codepoint in the downlink grant.
 18. Themethod in accordance with claim 17, wherein the codepoint indicating theone-bit group identifier N_(ID) ^(group) is one of the followingcodepoints defined DCI format 2A: a transport block to codeword(TB-to-CW) swap bit, and a new data indicator (NDI) bit of a disabledtransport block (TB), and wherein the other of the codepoints defined inDCI format 2A that is not used to indicate the one-bit group identifierN_(ID) ^(group) is used to indicate a stream index.
 19. The method inaccordance with claim 17, wherein the one-bit group identifier N_(ID)^(group) is indicated by a transport block to codeword (TB-to-CW) swapbit defined in DCI format 2A, and a stream index is indicated by a newdata indicator (NDI) bit of a disabled transport block (TB) defined inDCI format 2A.
 20. The method in accordance with claim 17, wherein theone-bit group identifier N_(ID) ^(group) and a stream index areindicated by a transport block to codeword (TB-to-CW) swap bit and a newdata indicator (NDI) bit of a disabled transport block (TB) defined indownlink control information (DCI), format 2A as follows: ReinterpretedReinterpreted NDI bit of TB-to-CW swap bit the disabled TB (group id,stream id) 0 0 (0, 0) 0 1 (0, 1) 1 0 (1, 0) 1 1 (1, 1).